1. Field of the Invention
The present invention relates generally to electrical discharge machining technologies and applications. More particularly, the present invention discloses an EDM apparatus and method for accomplishing combined electro-erosion and mechanical sawing of such as explosive ordinance having an outer steel casing surrounding such as a granular (RDX) or epoxy based explosive.
2. Description of the Prior Art
The prior art is well documented with sundry examples of electrical discharge machining (EDM) apparatuses and methods. As is generally known in the art, the objecting of EDM technology is to accomplish, such as through the provision of a suitably configured and constructed wire, electro-erosion cutting of a specified workpiece. The workpiece is further typically consisting of a metallic based material amenable to spark erosive cutting by the wire, and upon passing a current through the wire which is arced to the workpiece, and so that, upon immersing the workpiece in a suitable electrically conductive and coolant/fluidic bath, eroded portions of the workpiece are carried away from the cutting zone established by the eroding wire.
Numerous applications of EDM technology are further known, such as alternative shaping and configuration of the wire electrode, and one example of this is disclosed in U.S. Pat. No. 4,766,280, issued to Groos. The Groos reference teaches providing projections and recesses in an electrode wire created by twisting the wire electrode, selected from a variety of polygonal cross sectional shapes such as square, rectangle, triangle, hexagon, etc., about its axis.
U.S. Pat. No. 4,418,263, issued to lnoue, teaches a combined method and apparatus for electroerosively wirecutting a conductive workpiece with a continuous wire electrode and which, in particular, includes the steps of feeding the wire electrode from a supply reel and subsequently shaping the electrode into a cross sectional contour (including such as square or triangular shapes) which is preselected in conjunction with the desired pattern of cut to be formed in the workpiece. The shaping means incorporated into Inoue ""263 may take the form of a drawing die or an electro-erosive wire-cutting electrode assembly.
A yet further subset category of EDM references deal with coating applications applied to the electrode wire and one example of this is set forth in U.S. Pat. No. 4,977,303, issued to Briffod which teaches coating a copper wire core with zinc, heating in an oxidizing atmosphere to simultaneously provide a copper-zinc-alloy layer over the copper core and a zinc oxide surface on the alloy layer. The oxide and alloy coated wire is then reduced in diameter to reduce the thickness of the alloy layer by about one-half of its initial thickness, the resulting electrode wire permitting a greater current density and a greater tractional force to be employed, yielding increased machining speed in the EDM process.
A final subset category of prior art, heretofore non-EDM related, deals with explosive disarming and decommissioning, in particular of shells or other hardened outer casings filled with explosive. A first example of a material-energized plasticized metal slug cutter for use within tubular cylinders, pipe or like structure, is set forth in U.S. Pat. No. 6,016,753, issued to Glenn. The cutter in Glenn includes the provision of explosive material initially disposed in a particular hourglass or dog-bone shape surrounded by a layer of explosive-plasticizable copper or similar material which becomes both heated to plasticity and imparted with kinetic energy upon explosive material detonation.
The hourglass/dog-bone shape of the explosive material provides focus or shaping of the copper metal into a confined slug pattern, enabling a clean and relatively low expended-energy cutting of a surrounding tubular cylinder into axial segments. The cutter further employs a cutting action inclusive of spalling at the outer surface of the cut tubing opposite the region of slug impact. Scaling of explosive material sizes, weights and shaped for differing tubular cylinder dimensions is disclosed along with a mathematical algorithm usable in cutting action prediction.
Finally, U.S. Pat. No. 6,113,343, issued to Goldenberg et al., teaches an explosives disposal robot having a wheeled platform with a winder mechanism and a turret mechanism carrying at least one manipulator arm, the arm in turn including such as an aiming and disrupter mechanism and a relocatable surveillance camera. In further relevant part, the robot is capable of controlled movement to or from a hazardous site and to either remove or destroy a target. A wrist and gripper mechanism employed with the robot operates, in combination with any or all of the described extension links, to facilitate dexterous operation.
The present invention teaches an EDM apparatus and method for accomplishing combined electro-erosion and mechanical sawing of explosive ordinance (explosives decommissioning), and such as further including an outer steel casing surrounding such as a granular (RDX) or epoxy based explosive and with the further provision of a detonator located at the head of the steel casing and communicable with the explosive material. The particular advantage of the present invention is that it provides a wire electrode which is both constructed and configured so that it serves the dual function of electro-erosive EDM cutting of the surrounding and metallic based jacket of the shell, combined with mechanical sawing (abrasion cutting) of the RDX or epoxy based explosive contained within the shell and in particular to safely sever from the shell the detonator located at the head of the shell.
An elongated wire electrode is provided and which is typically unreeled in a generally circular cross sectional shape from a supply spool. The wire electrode is, as is known in the art, constructed of an electrically conductive metallic composition and, in one preferred application, may further include an outer and softer layer of metal and an inner core of a harder metal.
Forming rollers are provided for imparting a desired and further polygonal cross sectional shape to the wire electrode. Opposing and guiding/forming surfaces of the rollers are further configured, in one application, to impart a triangular cross sectional shape to the wire electrode, as well as in addition texturing the outer surfaces of the electrode such that the textured surface further exhibits a plurality of individual teeth.
Pairs of feed and take-up rollers are positioned on opposite sides of the workpiece and such that the wire electrode is guidably extended between each of the pairs of rollers in a direction generally perpendicular to a machining zone defined in relation to the workpiece. During the machining stage, an electrical current is passed to the electrode, typically through one of the feed or take-up rollers, and in order to generate a desired ionization channel or arc relative to the outer metal jacket of the shell and to electro-erode/section the metal. A die-electric bath may also be provided and, in combination with the particular electrical components and variables of current and voltage delivered to the machining zone, prevent inadvertent detonation of the shell during decommission machining.
Upon successfully piercing/sectioning the outer jacket, the configured teeth of the electrode abrade against the inner RDX (or other suitable non-metallic and explosive core interior) material and so that, upon continuous advancing of the wire electrode across the machining zone, the teeth mechanically section the inner core, contemporaneous with the electro-erosion of the outer/annular configured metallic jacket layer, and in order to section a portion of the shell containing the detonator, thereby decommissioning the shell.
A pair of pulling pinch rollers are arranged subsequent to the take-up rollers and re-direct the used electrode to a take up spool for rewinding and disposal. Tensioning members are located; upon both the feed and take-up sides of the electrode and are preferably provided in the form of potentiometer rollers, such as located between the reel spool and forming rollers and between the take-up rollers and pulling pinch rollers, respectively. Additional features include an advancing head mechanism for actuating the wire electrode in a direction substantially perpendicular to an extending length across the machining zone and so that the system can provide combined advancement/retraction of the electrode wire, combined with its continuous longitudinal and redirecting advancement between the spools and across the various forming, feed, take-up, pinching and tensioning rollers.
A method for accomplishing combined electro-erosion and mechanical cutting of the workpiece/explosive shell is also disclosed and includes the steps of unreeling a supply of the elongated wire electrode, forming the specified polygonal and cross sectional (e.g., triangular) shape of the electrode contemporaneous with texturing the outer surface of the electrode with such as a plurality of individual-teeth. Additional steps include guidably advancing, in longitudinal fashion, the wire electrode across a machining zone defined between the wire electrode and the workpiece, supplying the electrical current to the electrode to create the desired electrical arc within the machining zone, and sectioning the RDX inner core upon the advancement and abrasion of the teethed outer surfaces of the electrode against and through the inner core. Yet additional method steps include the immersing of the machining zone with the die-electric fluid, as well as perpendicular advancement of the electrode across the machining zone and through the diameter of the shell.